(a) Field of the Invention
This invention relates to frictional forced power transmission belts for transmitting power with their belt body wound around and in contact with a pulley, and relates to belt drive systems with the same.
(b) Description of the Related Art
Widespread use is made of serpentine belt drive systems for transmitting power from a crank shaft of an automotive engine to accessories such as a power steering, an air compressor and an alternator via a single V-ribbed belt in order to reduce the space for an engine room. Under these circumstances, such a V-ribbed belt is required to have a high power transmission capacity. In addition, the V-ribbed belt is also required to have a high noiselessness during belt run for the pursuit of a comfortable ride on a vehicle and other purposes. For these purposes, a typical V-ribbed belt is reinforced by short fibers mixed in a compression rubber layer that makes contact with pulleys so as to be oriented in a belt widthwise direction, and the short fibers protrude beyond the belt surface to reduce the coefficient of friction of the belt surface, resulting in reduced noise production and improved abrasion resistance.
Japanese Unexamined Patent Publication No. 7-63242 discloses a technique that a rib rubber layer of a V-ribbed belt made of hydrogenated acrylonitrile-butadiene rubber has a double-layered structure of a rib bottom and a rib top, short fibers are mixed into the hydrogenated acrylonitrile-butadiene rubber forming the rib bottom and oriented substantially in the belt widthwise direction, and unsaturated carboxylic acid's metal salt is compounded into the hydrogenated acrylonitrile-butadiene rubber forming the rib top. This publication describes that the above technique can provide a long-life V-ribbed belt that even in use under severe conditions such as rises in environmental temperature, has an excellent heat resistance, abrasion resistance and flexural fatigue resistance and does not cause any trouble such as malfunction due to abrasion.
Japanese Unexamined Patent Publication No. 2003-12871 discloses a V-ribbed belt formed of an elastic body layer including an adhesion rubber layer in which a cord is embedded along the belt lengthwise direction and a compression rubber layer, wherein out of the elastic body layer consisting of the adhesion rubber layer and the compression rubber layer, at least the compression rubber layer is made of a vulcanizate of an ethylene-α-olefin elastomer compound, the ethylene content of the ethylene-α-olefin elastomer is 60 to 75 mass %, one or more kinds of short fibers of 0.5 mm to 3 mm length are contained as reinforcing fibers in the compression rubber layer, and the total amount of addition of the short fibers is 10 to 30 parts by mass to 100 parts by mass of the ethylene-α-olefin elastomer. This publication describes that such a short fiber-containing rubber composition excellent in sheetability is used at least for the compression rubber layer, thereby providing a high-durability power transmission belt having excellent flexural fatigue resistance and heat resistance, cold resistance, abrasion resistance and sticking abrasion resistance.
The short fibers for use in V-ribbed belts are fabricated by cutting long fibers, and need to be subjected to adhesion treatment in order to be given adhesiveness to the rubber, resulting in high material unit cost. This is one of the factors of rise in the belt material cost.
V-ribbed belts are fabricated by applying heat and pressure to materials including an unvulcanized rubber sheet, a woven fabric and a cord wrapped or wound around a cylindrical mould. In this case, as the unvulcanized rubber sheet forming a rib rubber part of a belt body, use is made of an unvulcanized rubber sheet in which short fibers are oriented substantially perpendicularly with respect to the direction of wrapping around the cylindrical mould. Such an unvulcanized rubber sheet in which short fibers are oriented in a single direction is fabricated by extending a massive, unvulcanized rubber containing short fibers in a sheet form by a calender roll or the like. In the unvulcanized rubber sheet thus fabricated, short fibers are oriented in the longitudinal direction of the sheet. Therefore, in fabricating a V-ribbed belt, the elongated unvulcanized rubber sheet containing short fibers cannot be used as it is, i.e., with its longitudinal side aligned with the direction of wrapping around the mould, and needs to be used by cutting it to a slightly shorter length than that of the mould and wrapping it around the cylindrical mould with both cut edges coming to both sides of a row of V ribs. In this way, in fabricating a V-ribbed belt, the step of cutting a rolled unvulcanized rubber sheet containing short fibers is needed. This becomes a factor that raises the belt production cost.